Electrogenerated Hydrogen Peroxide Research Articles

Electrochemical removal of imidacloprid on different anodes with in-situ H2O2 generation: Optimizing conditions for rapid degradation and safe byproducts

Imidacloprid is a neonicotinoid insecticide with the highest detection frequency in aquatic environments. To address its issue, the degradation of imidacloprid present in a commercial sample was investigated through the efficiencies of BDD, Pt, and MMO-RuO2-TiO2 anodes, using electrochemical oxidation with hydrogen peroxide electrogeneration (EO-H2O2), and employing a gas diffusion electrode (GDE) as the cathode. Among the anodes tested, BDD provided the best results, with complete degradation of imidacloprid after 40 min using pH 7, 67 mA cm−2, and Na2SO4 as the supporting electrolyte, for all the initial imidacloprid concentrations investigated. Additionally, tests were performed using IMD at low concentrations in different matrices. Replacing Na2SO4 with NaCl as the supporting electrolyte resulted in significantly increased degradation using the Pt (51.0–92.0 %) and MMO (49.0–88.0 %) anodes. LC-MS analyses confirmed the complete degradation of imidacloprid, with the data obtained enabling the proposal of the structures of two degradation products. Toxicity analysis using ECOSAR software showed that imidacloprid could cause acute and chronic toxicity for the organisms studied, while degradation product I did not show any toxicity, and degradation product II was classified as harmful to fish. The findings indicated that under optimized conditions, the three anodes have a high potential for use in EO-H2O2 systems for the removal of imidacloprid present in water matrices.

Synthesis of activated carbon from sugarcane bagasse using blends of hydroxides for maximizing reaction targeted at obtaining hydrogen peroxide

This study investigates the potential reutilization of sugarcane bagasse (SCB) – a highly abundant residue generated from the sugar and ethanol industries. Activated carbon (AC) with optimized selectivity toward hydrogen peroxide (H2O2) electrogeneration was obtained by applying a customized process that involved the impregnation of the residue with KOH and NaOH and thermal activation. To optimize the properties of the AC, the following synthesis parameters were evaluated: proportion of KOH/NaOH used in the impregnation process, activation temperature, holding time (of the activation temperature), and concentration of activating solution. The optimized condition obtained was NaOH at 10 %m/v, activation temperature of 650 °C, and holding time of 60 min; this condition was found to be more sustainable than that of the traditional processes employed in obtaining black carbon. The near-optimal condition generated an AC with outstanding wettability, high amount of oxygenated groups on the surface, and a surface area of 121.2 m2 g−1, with good theoretical selectivity toward H2O2 electrogeneration (90 % at −0.4 vs. RHE) and an onset potential of +0.3 vs RHE. Our findings show that the SCB-derived AC material could be used as an environmentally friendly and economical alternative to conventional petroleum-derived carbon materials commonly used in H2O2 electrogeneration and as a support material for other active materials. The study shows that the precise equilibrium of the physical attributes of the carbon material and the chemical composition of its surface, influenced by the activation process, are key factors that affect catalytic efficiency in the in situ electrogeneration of H2O2.

Iron Nanoparticle-Incorporated Laser-Induced Graphene Filters for Environmental Remediation via an In Situ Electro-Fenton Process.

Laser-induced graphene (LIG) has garnered much attention due to its facile and chemically free fabrication technique. Metal nanoparticle incorporation into the LIG matrix can improve its electrical and catalytical properties for environmental application. Here, we demonstrate the fabrication of nanoscale zerovalent iron (nZVI) nanoparticle-incorporated LIG (Fe-LIG) and sulfidized-nanoscale zerovalent iron (S-nZVI) nanoparticle-incorporated LIG (SFe-LIG) surfaces. The sheets were first fabricated to investigate nanoparticle loading, successful incorporation in the LIG matrix, and electrochemical performance as electrodes. Fe-LIG and SFe-LIG sheets showed ∼3-3.5 times more charge density as compared with the control LIG sheet. The XPS and its deconvolution confirmed the presence of nZVI and S-nZVI in the Fe-LIG and SFe-LIG surfaces, which can generate in situ hydroxyl radical (•OH) via iron activation of electrogenerated hydrogen peroxide (H2O2) in short in situ electro-Fenton process. After confirmation of the successful incorporation of iron-based nanoparticles in the LIG matrix, filters were fabricated to demonstrate the application in the flow-through filtration. The Fe-LIG and SFe-LIG filters showed ∼10-30% enhanced methylene blue removal under the application of 2.5 V at ∼1000 LMH flux. The Fe-LIG and SFe-LIG filters also showed complete 6-log bacteria and virus removal at 2.5 and 5 V, respectively, while the LIG filters showed only ∼4-log removal. Such enhanced removal by the Fe-LIG and SFe-LIG filters as compared to LIG filters is attributed to the improved charge density, electrochemical activity, and in situ electro-Fenton process. The study shows the potential to develop catalytic LIG-based surfaces for various applications, including contaminant removal and microbial inactivation.

Degradation of diethyl phthalate by photolysis of hydrogen peroxide electrogenerated using a Printex L6 carbon modified with Benzophenone cathode in an improved tangential flow cell

In this work, a gas diffusion electrode (GDE) made of Printex L6 carbon modified with 2.0% w/w of benzophenone-3,3′,4,4′-tetracarboxylic dianhydride (PL6C/BTDA 2%) was employed as cathode in a new 3D printed electrochemical cell with tangential flow. With this configuration, the performance of the technology was evaluated for hydrogen peroxide (H2O2) electrogeneration and remediation of aqueous wastes contaminated with diethyl phthalate (DEP) using different H2O2-based advanced oxidation processes (AOPs). The electrogeneration study was carried out varying the current density applied to the system, and it was found that 50 mA cm-2 was the best performing value, resulting in remarkable Faradaic efficiencies of nearly 100%. This led to the production of higher amounts of H2O2 (442.5 mg L-1) in 90 minutes at an acceptable energy consumption (8.5 kWh kg-1) compared to values reported in the literature. Based on these findings, H2O2-based AOPs were employed to investigate the removal of DEP in cathodic compartment, including mediated electrochemical degradation with electrogenerated H2O2 (e-H2O2) and the integration of this technology with ultraviolet-C (UVC) photolysis (e-H2O2/UVC). The integrated e-H2O2/UVC obtained the best performance compared to single photolysis and e-H2O2, leading to the total elimination of DEP (90 μmol L-1) within only 30 min of treatment, reaching the highest kinetic rate constant (0.3 min-1). Fifteen by-products, generated through oxidation processes studied, were successfully identified by LC-MS/MS, enabling the proposal of the degradation mechanism of DEP.

Electrocatalytic hydrogen peroxide generation using WO3 nanoparticle-decorated sodium niobate microcubes

The current work studies the electrocatalytic performance of NaNbO3 microcubes decorated with WO3 nanoparticles on Printex L6 at varying concentrations (1%, 3%, 5%, and 10% by weight) for H2O2 electrogeneration aiming for future use in electrochemical advanced oxidation processes for organic pollutant degradation·H2O2 electrogeneration was studied using oxygen reduction reaction (ORR) with the rotating ring-disk electrode (RRDE) technique. Electrochemical results revealed an improvement in H2O2 electrogeneration for the NaNbO3@WO3/C materials compared to that achieved with Printex L6 carbon. Notably, the 5% NaNbO3@WO3/C electrocatalyst exhibited a higher ring current for oxygen reduction reaction and promoted a 2.1-electron transfer, facilitating a higher rate of H2O2 electrogeneration through the 2-electron mechanism. Also, enhancing oxygen-containing functional groups has shown the capability to thoroughly adjust characteristics and enhance active sites, increasing H2O2 electrogeneration. These findings suggest that 5% NaNbO3@WO3/C electrocatalysts hold promise for in situ hydrogen peroxide electrogeneration.

Unlocking the Potential of Nanobubbles: Achieving Exceptional Gas Efficiency in Electrogeneration of Hydrogen Peroxide (Small 3/2024)

Unlocking the Potential of Nanobubbles: Achieving Exceptional Gas Efficiency in Electrogeneration of Hydrogen Peroxide (Small 3/2024)

Microwave-Assisted Synthesis of Nitrogen-Doped Carbon Catalysts for Oxygen Reduction Reaction with Tunable Selectivity

The oxygen reduction reaction (ORR) is the core reaction in electrocatalysis systems such as fuel cells, metal-air batteries and hydrogen peroxide (H2O2) electro-generation. The ORR reaction mechanism has two possible pathways, namely, two-electron (2e−) or four-electron (4e−) processes that enable a reduction of oxygen into H2O2 or water (H2O), respectively. Both paths are useful where the former can provide on-site direct production of H2O2 and the latter is desired in fuel cells and batteries since it enables higher energy efficiency. Optimal ORR electrocatalyst should exhibit high activity, selectivity, stability, and low cost. Carbon materials modified with heteroatoms (e.g. nitrogen (N)) are considered potential alternatives for costly noble metal catalysts including Pt for ORR in fuel cells, and Au for the ORR to H2O2 (1,2). The typical synthesis procedure for the porous nitrogen-doped carbons (N–C) is based on the single or multiple pyrolysis steps of nitrogen-rich carbon precursor. The reactions required a pyrolysis step at the temperature range of 500-1200 °C and timing of one to tens of hours. Such processes showed a highly negative environmental impact due to high energy consumption. The production of 1 ton of activated carbon from lignocellulosic biomass feedstock requires 669.83 kWh (equivalent to an emission of 62.78 tons of CO2) (3). The synthesis of the N–C by microwave (MW) irradiation can reduce energy usage and ensure a more environmentally sustainable and economically viable approach. This procedure necessitates non-transparent materials to electromagnetic waves that can convert MW energy into heat and simultaneously enable the carbonization of the starting material.This work investigated the electrocatalytic activity towards ORR for N–C–MW catalysts derived from polyaniline (PANI) prepared in a one-step MW carbonization approach. PANI was selected due to two reasons: (i) N–C made by thermal pyrolysis of PANI showed improved electrocatalytic activity toward ORR where both the 4e− and the 2e− electron transfer pathways are feasible depending on the nature of active sides (4), (ii) PANI displayed good MW adsorption properties (5). The work aimed to identify the influence of the MW reaction condition on the resulting structure of the N–C–MW and the direction of the ORR. The N–C–MW samples were prepared under MW power of 450 and 800 W and time of 70, 140 and 210 s. The ORR activity of N–C–MW samples was investigated by cyclic voltammetry in the alkaline media (O2-saturated 0.1 M KOH). The experiment was performed in a three-electrode configuration composed of a rotating ring (Pt)–disk (glassy carbon) electrode (RRDE), a graphite rod as the counter electrode and a reversible hydrogen electrode (RHE) as the reference electrode. An influence of catalyst loading on disk electrode (0.05, 0.1 and 0.2 mg/cm2) was analyzed. All investigated MW reaction conditions resulted in the formation of porous disordered carbon structures with nitrogen and oxygen functionalities confirmed by X-ray photon-electron spectroscopy. The shorter time (70 s) and lower power (450 W) of MW treatment resulted in the formation of structures with a low carbonization rate and simultaneously a relatively poor catalytic activity for ORR (an onset potential of ∼0.65 V vs RHE). The samples carbonized under moderate (power of 450 W and 800 W, time of 140 s) and severe (power of 450 W, time of 210 s) reaction conditions showed higher selectivity to H2O2 or water H2O, respectively. The selectivity of 80 % to H2O2 was achieved for the N–C–MW-800W-140s sample at the potential of 0.6 V vs RHE at the catalyst loading of 0.05 mg/cm2. The results showcase the potential of MW carbonization in producing ORR electrocatalysts with diverse functionalization, leading to modified reaction selectivity that can be utilized in various electrocatalytic applications. Acknowledgments The research leading to these results was supported by the Johannes Amos Comenius Programme, European Structural and Investment Funds, project 'CHEMFELLS V‘ (No. CZ.02.01.01/00/22_010/0003004). References Yang, S. et al., Toward the decentralized electrochemical production of H2O2: A focus on the catalysis. ACS Catalysis, 2018.Bouleau, L. et al., Best practices for ORR performance evaluation of metal-free porous carbon electrocatalysts. Carbon, 2022.Wang, YX. et al., Quantifying environmental and economic impacts of highly porous activated carbon from lignocellulosic biomass for high-performance supercapacitors. Energies, 2022.Silva, R. et al., Efficient metal-free electrocatalysts for oxygen reduction: Polyaniline-derived N- and O-doped mesoporous carbons. Journal of the American Chemical Society, 2013.Oyharçabal, M. et al., Influence of the morphology of polyaniline on the microwave absorption properties of epoxy polyaniline composites. Composites Science and Technology, 2013. Figure 1

Photo-Chemical Sucralose Degradation in an Aqueous Medium Using a Photo-Fenton System Equipped with Stainless Steel Mesh Cathodes Modified By Nanostructured TiO2- and C|TiO2-Based Films for Continuous Electro-Generation of H2O2

Artificial non-caloric sweeteners are non-bioassimilable substances that pass through the human body without biochemical changes. Sucralose, for instance, is 600 times sweeter than natural sucrose, so it is widely used in beverages and processed food products without regulation in many countries. Its environmental persistence of 337 days in sludge allows inferring that these substances can adversely affect the environment in the short or long term, thus classifying sucralose as an emergent pollutant. In this work, stainless steel (SS) mesh working electrodes were modified by TiO2- or C|TiO2-based nanoparticulate films (where C is carbon Vulcan). Both types of electrodes were employed as cathodes for the electro-generation of hydrogen peroxide (H2O2), which was the chemical precursor for photochemical producing •OH radicals able for sucralose degradation in a photo-Fenton system equipped with a 254 nm light source. Preparation of TiO2- and C|TiO2-based cathodes was performed by electrophoretic deposition method (EPD, 2 V/cm for 40 s) on AISI 304 SS mesh, followed by sintering at 450°C for 1h in the air. The EPD process was performed using aqueous colloidal suspensions containing wt./wt. ratios of C/TiO2 = 1/100 and 1/10, or TiO2 without C for comparison purposes. H2O2 electro-generation was carried out via Reaction 1 utilizing a two-electrode cell (3V-cell polarization) containing sucralose dissolved in a pH 2 aqueous sulfates buffer solution perpetually bubbled by air (volumetric flow rate of 17 mL/s) containing gaseous O2. In all the cases, a Ti grade 2.0 rod anode was immersed in the electrolyte medium with one of the following cathodes: SS* (polished, degreased, and heated at 450°C for 1h in the air as control electrode), SS||TiO2 and SS||C|TiO2 (wt./wt. ratios of C/TiO2 = 1/100 or 1/10). Furthermore, the cell was illuminated by a 254 nm lamp in order to continuous promotion of the photo-chemical Reaction 2.O2 + 2H+ + 2e- → H2O2 ...............(1)H2O2 254mn→ 2°OH...................... (2)Sucralose degradation efficiencies were registered based on the cathodes employed for continuous H2O2 electro-generation. Furthermore, the relative use time was also registered for each cathode. A comparison of these results reveals that when employed SS*, SS||TiO2, and SS||C|TiO2 (wt./wt. ratio of C/TiO2=1/100) cathodes the sucralose degradation achieved efficiencies over 90% (i.e. 99.1, 96.8, and 91.3%, respectively). In contrast, SS||C|TiO2 (wt./wt. ratio of C/TiO2=1/10) cathodes showed a sucralose degradation efficiency of only 88.6%. Furthermore, the SS||TiO2 and SS||C|TiO2 cathodes showed durability 3 times higher than for the SS* cathodes, and 1.8 times higher than for SS||C|TiO2 (wt./wt. ratio of C/TiO2=1/10). These observations indicated that both, SS||TiO2 and SS||C|TiO2 cathodes are strong candidates for assembling more efficient photo-Fenton systems for the degradation of sucralose and other artificial sweeteners.

Degradation of real lindane wastes using advanced oxidation technologies based on electrogenerated hydrogen peroxide

In this work, hydrogen peroxide (H2O2) is produced using an optimized electrochemical cell equipped with a gas diffusion electrode (GDE) as cathode, reaching efficiencies as high as 20.1%, when operating in a single compartment configuration, which increases up to the range 50–60, when a proton exchange membrane is used to separate the anodic and cathodic compartments, pointing out the great significance of the anodic oxidation of H2O2 and the scavenging effects of the oxidants produced on the anode surface. As compared to previous materials tested, the GDE implemented in this cell underwent a more sustainable manufacturing procedure and exhibited an outstanding performance. The H2O2 produced electrochemically is dosed to the real leachate of an industrial dump, strongly polluted with derivatives of lindane. This waste is associated to the operation of a large facility in the seventies and contains different isomers of hexachlorocyclohexane and other chlorinated hydrocarbons, produced during the ageing of the dump. Effects of the addition of iron (II) sulfate salts and irradiation of UVC were also evaluated. All electrochemically-assisted technologies evaluated (named as chemical (EACO), Fenton (EAFO), photolysis (EAPO) and photo-Fenton (EAPFO) oxidations) were able to successfully remove the pollutants, although with important differences in the efficiencies reached. Results demonstrate that EACO, that is, oxidation by molecular H2O2 is the most effective treatment for the treatment of this type of wastes, pointing out that activation of H2O2 to hydroxyl radicals, either by electrochemically assisted Fenton or photolysis is not positive for this waste. As well, among the different pollutants contained in the raw waste, removal of hexachlorocyclohexane (HCHs) and non-chlorinated volatile organic compounds (VOCs) stands out (both groups being the primary species contained in the wastes). These results are very important not only because of the outstanding productions of H2O2 reached with the novel approach of electrochemical cell used, but also because of the implications of the mechanistic understanding of the attack of H2O2 species in the design of a full-scale application to remediate this real important problem.

Performance of Electro-Fenton Process for Phenol Degradation Using Nickel Foam as a Cathode

Toxic substances have been released into water supplies in recent decades because of fast industrialization and population growth. Fenton electrochemical process has been addressed to treat wastewater which is very popular because of its high efficiency and straightforward design. One of the advanced oxidation processes (AOPs) is electro-Fenton (EF) process, and electrode material significantly affects its performance. Nickel foam was chosen as the source of electro-generated hydrogen peroxide (H2O2) due to its good characteristics. In the present study, the main goals were to explore the effects of operation parameters (FeSO4 concentration, current density, and electrolysis time) on the catalytic performance that was optimized by response surface methodology (RSM). According to the results, nickel foam made an excellent choice as cathode material. The pH value was adjusted at 3 and the airflow at 10 L/h for all experiments. It was found that the optimal conditions were current density of 4.23 mA/cm2, Fe2+ dosage of 0.1 mM, and time of 5 h to obtain the removal rates of phenol and chemical oxygen demand (COD) of 81.335% and 79.1%, respectively. The results indicated that time had the highest effect on the phenol and COD removal efficiencies, while the impact of current density was the lowest. The high R2 value of the model equation (98.03%) confirmed its suitability.

Multifunctional and sustainable soot-modified nanofibrous membrane for adsorption, sensing and hydrogen peroxide electrogeneration

The incineration of plastics and biomass is an efficient alternative to reduce the amount of solid waste and is also beneficial for energy production. Soot is one of the main byproducts generated during solid waste incineration, and so far, it has been treated as a pollutant. However, soot is an interesting nanostructured material displaying high specific surface area and chemical reactivity. In this work, soot produced by incomplete burning of plastic materials was combined with polymer nanofibers resulting in a multifunctional membrane explored for pollutant adsorption, sensing of organic pollutants, and in the electrogeneration of hydrogen peroxide. Specifically, soot was immobilized onto polyamide 6 nanofibrous membranes (NFM) produced by solution blow spinning following two different approaches: pre-synthesis and post-synthesis modification, and then the effect of soot chemical activation with NaOH was investigated. The adsorption tests showed that the chemical activation was essential to increase efficiency by improving its hydrophilicity and generation of adsorption sites. The experimental and calculated batch adsorption efficiency towards methylene blue was 94.33 mg/g and 37.71 mg/g, respectively. The adsorption efficiency in the fixed bed was 8.00 mg/g. The functional NFMs maintained their efficiency for at least ten adsorption cycles, increasing their economic viability. Furthermore, the NFMs were applied as flexible and free-standing electrodes for detecting methylene blue with a limit of detection of 2.4 nmol/L. The average per-electrode cost was estimated to be US$0.04. Finally, the NFM also demonstrated the ability to generate H2O2 in situ. Altogether, these results suggest that the immobilization of soot onto nanofibrous membranes is an efficient strategy for developing multifunctional and sustainable materials towards environmental applications.

Unlocking the Potential of Nanobubbles: Achieving Exceptional Gas Efficiency in Electrogeneration of Hydrogen Peroxide.

The electrogeneration of hydrogen peroxide (H2 O2 ) via the oxygen reduction reaction is a crucial process for advanced water treatment technologies. While significant effort is being devoted to developing highly reactive materials, gas provision systems used in these processes are receiving less attention. Here, using oxygen nanobubbles to improve the gas efficiency of the electrogeneration of H2 O2 is proposed. Aeration with nanobubbles is compared to aeration with macrobubbles under an identical experimental set-up, with nanobubbles showing a much higher gas-liquid volumetric mass transfer coefficient (KL a) of 2.6 × 10-2 min-1 compared to 2.7 × 10-4 min-1 for macrobubbles. Consequently, nanobubbles exhibit a much higher gas efficiency using 60% of O2 delivered to the system compared to 0.19% for macrobubbles. Further, it is observed that the electrogeneration of H2 O2 using carbon felt electrodes is enhanced using nanobubbles. Under the same dissolved oxygen levels, nanobubbles boost the reaction yield to 84%, while macrobubbles yield only 53.8%. To the authors' knowledge, this is the first study to investigate the use of nanobubbles in electrochemical reactions and demonstrate their ability to enhance gas efficiency and electrocatalytic response. These findings have important implications for developing more efficient chemical and electrochemical processes operating under gas-starving systems.

Sodium niobate microcubes decorated with ceria nanorods for hydrogen peroxide electrogeneration: An experimental and theoretical study

The present work investigates the catalytic activity of NaNbO3 microcubes decorated with CeO2 nanorods on carbon (1 %, 3 %, 5 %, and 10 % w/w) for H2O2 electrogeneration. The crystalline phases and the morphology of the materials were identified with scanning electron microscopy, transmission electron microscopy, X‐ray diffraction and X-ray Photoelectronic spectroscopy. Contact angle measurements were performed to characterize the hydrophilicity of each material. The H2O2 electrogeneration was assessed by oxygen reduction reaction using the rotating ring-disk electrode technique. Electrochemical characterization results shown an enhancement on the H2O2 electrogeneration by NaNbO3 @CeO2/C-based materials compared to what was obtained with pure Vulcan XC72. The 1 % NaNbO3 @CeO2/C electrocatalyst presented the lower starting potential for the ORR and a 2.3 electron transfer, favoring the 2-electron mechanism and providing a higher H2O2 electrogeneration rate. Also, the enhancement of oxygen-containing functional groups showed the potential to comprehensively tune properties and optimize active sites and, consequently, increases the H2O2 electrogeneration. Density functional theory calculations indicated that NaNbO3 and CeO2 surfaces have a similar low theoretical overpotential for this reaction and that CeO2 improves the catalyst facilitating the electron transfer. These results indicate that NaNbO3 @CeO2/C-based electrocatalysts are promising materials for in situ H2O2 electrogeneration.

Using ZrNb and ZrMo oxide nanoparticles as catalytic activity boosters supported on Printex L6 carbon for H2O2 production

Oxygen reduction reaction (ORR) is an important reaction which is widely applied in advanced oxidative processes (AOP) through the in-situ electrogeneration of hydrogen peroxide. Oxygen gas can either be reduced to hydrogen peroxide via two-electron pathway or be converted to water in a competitive way via four-electron pathway. In this study, we report the effective enhancement of H2O2 generation in K2SO4 0.1 mol/L (pH 2) through the application of Printex L6 carbon (PL6C) modified with zirconium/niobium (ZrNb) and zirconium/molybdenum (ZrMo) oxides compared to unmodified PL6C. The proposed catalysts were prepared by the polymeric precursors synthesis method (on carbon). The catalysts were analyzed by X-ray fluorescence (FRX), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS), and were electrochemically characterised by cyclic voltammetry (CV) and hydrodynamic linear sweep voltammetry (LSV). The electroactivity of ZrNb/PL6C and ZrMo/PL6C oxides was analyzed in the ratio of 50/50 w/w. The results obtained from the electrochemical characterisations of the electrodes showed that the application of 5% ZrNb/PL6C and 1% ZrMo/PL6C yielded H2O2 selectivity of 84.3 and 77%, respectively, compared to 84.3% recorded for the unmodified PL6C. Also, based on the application of a determined current density, 5% ZrNb/PL6C and 1% ZrMo/PL6C recorded a potential shift of 200 and 400 mV to less negative potentials, respectively, compared to the unmodified PL6C, which implies in less energy consumption. The results obtained from the morphological and surface characterisations of the materials pointed to a practically homogeneous distribution of ZrO2, Nb2O5, and MoO3 with particle size of ca. 5 nm on the PL6C surface compared to the unmodified PL6C which exhibited particle size of ca. 30–50 nm.

Activity and stability of bifunctional perovskite/carbon-based electrodes for the removal of antipyrine by electro-Fenton process

Bifunctional perovskite/carbon-black(CB)/polytetrafluoroethylene(PTFE) electrodes for electro-generation and catalytic decomposition of hydrogen peroxide to oxidizing hydroxyl radicals have been fabricated. These electrodes were tested for electroFenton (EF) removal of antipyrine (ANT) as a model antipyretic and analgesic drug. The influence of the binder loading (20 and 40 wt % PTFE) and type of solvent (1,3-dipropanediol and water) was studied for the preparation of CB/PTFE electrodes. The electrode prepared with 20 wt % PTFE and water exhibited a low impedance and remarkable H2O2 electro-generation (about 1 g/L after 240 min, a production rate of ca. 6.5 mg/h·cm2). The incorporation of perovskite on CB/PTFE electrodes was also studied following two different methods: i) direct deposition on the CB/PTFE electrode surface and ii) addition in the own CB/PTFE/water paste used for the fabrication. Physicochemical and electrochemical characterization techniques were used for the electrode's characterization. The dispersion of perovskite particles in the own electrode matrix (method ii) exhibited a higher EF performance than the immobilisation onto the electrode surface (method i). EF experiments at 40 mA/cm2 and pH 7 (non-acidified conditions) showed ANT and TOC removals of 30% and 17%, respectively. The increase of current intensity up to 120 mA/cm2 achieved the complete removal of ANT and 92% of TOC mineralisation in 240 min. The bifunctional electrode also proved high stability and durability after 15 h of operation.

Evaluating key properties of carbon materials as cathodes for the electrogeneration of hydrogen peroxide

Twenty two carbon materials of different origins (e.g., graphite, graphene, carbon black, hydrochars, activated carbons, carbon nanotubes and nanofibers) and with varied physicochemical characteristics (e.g., electrical conductivity, structural order, surface functionalization, porosity) were investigated as cathodes in the electrochemical production of hydrogen peroxide. A screening of the electrocatalytic performance was carried out in 0.2 cm2 (inks casted on a glassy carbon) and 4 cm2 electrodes (Toray paper). The highest H2O2 production yields were obtained for carbon nanotubes and carbon nanofibers, outperforming common carbon benchmarks for this application -i.e., carbon black, carbon felt-. Furthermore, a good catalytic activity was obtained with low-cost and disordered carbon cathodes with moderate electrical conductivity and density of structural defects (e.g., nanoporous carbons), both in terms of overall production rate, selectivity and energy consumption. Data also revealed that the H2O2 production yield and the faradaic efficiency are closely related to the structural parameters of the carbon materials (i.e., density of structural defects), rather than to the electrical conductivity, composition or porous features. An AD/AG threshold value of 1.5 can be used to discriminate the electrocatalytic activity of carbon cathodes for the production of H2O2 through a 2e-ORR, in terms of high production rates and good faradaic efficiencies.

Multiphysics modeling of flow-through advanced oxidation photoreactors with in-situ hydrogen peroxide electrogeneration

Advanced oxidation processes (AOPs) commonly use chemicals such as hydrogen peroxide (H2O2) in combination with ultraviolet (UV) radiation to produce hydroxyl radicals (·OH). As supply chain management and storage of concentrated H2O2 is challenging, in recent years, in situ H2O2 generation systems are gaining attention. These systems are in early stages of research and development, and a numerical model can help accelerate the development of highly efficient systems. In this work, for the first time, we describe a mechanistic multiphysics model to simulate a flow-through electrochemical AOP photoreactor with in situ H2O2 electrogeneration and UV radiation. The electrochemical, hydrodynamic, radiation, and kinetic phenomena were incorporated into the model. The model showed good agreement with the experimental results over a wide range of flow rates (5% average difference in 35–95 mL min–1) and current densities (9% average difference 7–34 mA cm–2). The computational model was verified with the experimental data obtained for the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D), and it was applied to study the performance of some design variations in terms of hydrodynamics and radiation. The results showed that implementing reflective walls will increase the UV fluence, which ultimately led to a 45% improvement in the contaminant removal.

Comparative efficiency study of photoanodes in the photocatalytic fuel cell integrated electro-Fenton hybrid system

Photoanode in photocatalytic fuel cell (PFC) plays an important role in the dual chamber PFC integrating electro-Fenton (EF) hybrid system (PFC-EF system) since the photo-excitation process on the photoanode will contribute to the electrons for electricity generation and electro-generation of hydrogen peroxide in EF process. Fabrication of different types of photoanodes were carried out by using anodizing and immobilization method, respectively. The fabrication methods significantly affected the efficiencies of photoanodes in the Amaranth treatment. The characterization of the fabricated photoanodes was carried out by X-ray diffraction and scanning electron microscopy. The immobilized ZnO/Zn photoanode achieved the highest degradation efficiencies in both PFC (80.36%) and EF (86.88%). The immobilized ZnO/Zn photoanode also contributed to the highest power density (4.545 μW cm−2).

Using a novel gas diffusion electrode based on PL6 carbon modified with benzophenone for efficient H2O2 electrogeneration and degradation of ciprofloxacin

The present study reports the development and application of a gas diffusion electrode (GDE) based on Printex L6 carbon modified with 2.0% benzophenone-3,3′,4,4′-tetracarboxylic dianhydride (PL6C/2.0%BTDA) for the efficient electrogeneration of hydrogen peroxide (H2O2) and degradation of ciprofloxacin (CIP) using different advanced oxidation processes (AOPs). The modified GDE was studied under different current densities and 25 mA cm−2 was found to be the most efficient current density, since the application of the modified GDE at this current density yielded higher amounts of H2O2, greater kinetic constant and lower energy consumption compared to unmodified GDE. Based on these results, the modified GDE was used for the degradation of CIP in alkaline solutions using different AOPs, including anodic oxidation (AO), UVC photolysis, and processes based on H2O2 electrogeneration (AO/e-H2O2/UVC and AO/e-H2O2). The AO/e-H2O2/UVC technique was found to be the most efficient among the AOPs investigated; the application of this technique led to the complete removal of CIP (75 µmol L–1) in 20 min of treatment, apart from yielding the highest kinetic constant rate and lower electrical energy per order (2.1 kWh m−3 order–1). The oxidation by-products generated during CIP degradation via AO/e-H2O2/UVC were successfully identified and a pathway for CIP degradation was proposed.

Electro - Fenton processes for Landfill leachate treatment using different electrode materials

Landfill leachate contains high concentration of pollutants and treatment of leachate is very challenging as the properties are very fluctuating with quantity and time. Due to presence of non-biodegradable pollutants advanced oxidation processes are found effective to treat landfill leachate. In this study, fresh leachate sample from Jambuva landfill site at Vadodara, Gujarat, India was collected and analysed for the initial characterization. Electro-Fenton process was applied for the treatment of landfill leachate to evaluate the COD removal and colour removal by two methods: i) An external ferrous source is added, and an oxygen-sparging cathode produces hydrogen peroxide., and ii) Using an oxygen-sparging cathode and a sacrificial anode, hydrogen peroxide and ferrous ion are electrogenerated. In the first method, Graphite was used as a cathode and Titanium as anode. In the second method, graphite was used as a cathode and Iron as anode. Continuous electro generation of hydrogen peroxide and Fe ions were measured to assess the efficiency of treatment process. In first method, maximum COD removal (58.22%) was obtained at current density 30 A/m2, FeSO4.7H2O dose of 1 mM and contact time of 150 mins with more than 98% colour removal. Whereas, in the second method, maximum COD removal (46.99%) was obtained at current density 40 A/m2 at contact time of 150 mins with more than 93% colour removal. The electro- Fenton process was found to be efficient for landfill leachate treatment.